In the scientific and technical literature, sugar-based surfactant molecules are well known. Among them, sucrose fatty acid esters, sorbitan esters and long-chain alkyl polyglucosides have been widely used in foods, personal care, and cosmetic and pharmaceutical applications. Some of these surfactants have also found wide acceptance in household and industrial cleaning applications and as lubricants.
Despite their wide use and acceptance, it is well known that ester-based surfactants are stable only over a limited range of pH, whereas alkyl glucosides are stable under alkaline and neutral conditions but not under acidic conditions.
Other disadvantages are associated with the methods used to obtain these derivatives. In the case of higher alkyl glucosides, transacetalization is necessary. Rather complicated and costly equipment must be used in order to obtain a sufficiently pure product. In the case of sugar-based esters, in particular sorbitan esters, expensive and toxic solvents or high reaction temperatures are required in order to obtain products with sufficiently high yield.
In order to improve the acidic stability of sugar-based surfactant compounds, a sugar alcohol ether was recently proposed in the document WO 2012/148530. This application describes a method for preparing these polyol ethers whereby a molten mass of polyol is reacted with a higher alkyl aldehyde under reductive alkylation conditions. Here again, difficult and extreme conditions are necessary, in combination with high-pressure equipment, in order to carry out the reductive alkylation reaction. In order to obtain the desired products, excess sugar alcohol relative to aldehyde is deemed necessary. This results in high energy consumption per mole of sugar alcohol ether.
Another group of sugar-based surfactant molecules is represented by long-chain alkyl cyclic acetals of sugars, as disclosed in several scientific and technical publications.
In Carbohydrate Research (1997) p. 85-92, higher alkyl cyclic acetals of sucrose, and methods for obtaining same, are described. The acetals thus obtained could be of interest in the detergents industry because these products are stable in basic and neutral media, unlike ester derivatives. Moreover, they had advantageous critical micelle concentration (CMC) values. In OPPI Briefs (1998) p. 460-464, an improved method for preparing such sucrose-based compounds was disclosed.
In the document U.S. Pat. No. 6,251,937 (FR2761991) and JAOCS (1994) p. 705-710, higher alkyl cyclic acetals of gluconic acid derivatives having surfactant properties in basic and neutral media are described. At the same time, they also exhibited strong hydrolysis in acidic medium.
In the patent EP 0 019 999, the preparation of higher alkyl cyclic acetals of sugar derivatives, in particular of sorbitol derivatives, is disclosed. Thus proposed is an improved method using acetic acid as reaction medium. This reaction produces a sorbitol alkyl acetal partially substituted with acetate groups. In this same document, reference is made to the U.S. Pat. No. 4,031,112. In the latter document, it is mentioned that the reaction conditions described therein are usable to prepare long-chain alkyl acetals of sorbitol. It was noted, however, as mentioned in the patent EP 0 019 999, that the conditions described cause extensive decomposition of the products and the reagents, whereby the product's yield and quality become commercially unacceptable.
In the U.S. Pat. No. 3,484,459, reference is made to the preparation of cyclic acetals of sorbitan. In this document, mention is made of a wide range of aldehydes and ketones as potential reagents. These acetalization reactions are used to collect residual 1,4-sorbitan from a mixture of hexitans, after separating the pure acetals by fractional distillation. The sorbitan acetal thus obtained is hydrolyzed, and 1,4-sorbitan is collected by crystallization. The acetalization is thus carried out with a large excess of reagent, using long reaction times. The conditions used are relatively unattractive in terms of methodology.
In light of the above, it is clear that the products and/or methods described with regard to higher alkyl cyclic acetals made from sugars show a certain number of gaps. Apart from the polyol ether described in WO 2012/148530, all the other sugar-based surfactant molecules are unstable or are insufficiently stable under acidic conditions, whereas in most cases the methods use solvents or reaction conditions that are not safe from an environmental point of view, and/or that consume a lot of energy and/or are not profitable from an industrial point of view.
Consequently, it is obvious that there remains an unsatisfied need to have sugar-based long-chain alkyl cyclic acetals that exhibit improved stability under acidic conditions, in combination with good emulsifying properties. Moreover, there also remains a need to have methods for preparing these compounds, methods that are acceptable for the environment, advantageous in terms of energy consumption, and easy to implement industrially.